A cellular network with a high penetration of devices, using the network to communicate with servers or other devices, may be overloaded by the devices flooding the signaling interfaces and wasting available system recourses. Many of these devices might not be time critical in the sense that it does not matter if the transfer of data is done directly or waits for a few minutes or even longer.
Mobile devices of different types use the same communication resources in radio access networks and some mobile devices may not be able to access the network due to high traffic created by other mobile devices. Some users of mobile devices are more sensitive to being denied communication, for example users making phone calls, while others, for example machine type communication transferring data, may not be negatively affected if the data transfer is delayed.
In a Global System for Mobile communication (GSM) network, access attempts from non time-critical communication may collide with access attempts for time critical communication. This could lead to overload situations where important traffic, such as voice calls, are lost due to high load on signaling interfaces generated by access attempts made for communication that is not time critical.
The GSM have mechanisms for controlling access, including so called Access Control Classes (ACC). In GSM, each mobile device is assigned an ‘Access Control Class’ that is coded in the Subscriber Identity Module (SIM) (see 3GPP 44.018 section 10.5.2.29 (RACH control parameters)). The control parameters for the Access Control Classes are broadcasted as a part of system information messages. The parameters specify if a class of mobile devices is allowed to access or barred from accessing the network. A mobile belonging to a barred access class is not allowed to send access bursts to the network, i.e. the mobile is configured so that it may not initiate a call or answer a page, but still may read system information etc. The access classes are randomly assigned (‘Access Control Class’ 0-9 that is used for public subscriptions).
These classes may be used to limit access during high traffic loads. For example, the operator of the network may block access for 20 percent of the mobile devices by barring two of the ten classes randomly. The network will then create the system information messages wherein the parameters of the two barred access classes are changed and set to indicate barring of these classes. The devices receiving the system information adjusts their access settings accordingly, so that devices belonging to a barred class will not initiate signaling by sending access bursts, and will not answer paging messages from the network.
The system information messages that are broadcasted includes channel information, access information, location information, base station identity etc. In a GSM system the BSS (Base Station Subsystem) broadcasts the system information messages to the mobile devices. The BSS comprises a BSC (Base Station Controller) and a BTS (Base Transceiver Station) and the system information messages are created in the BSC and transferred to the MS (mobile devices) via the BTS, which transmit the system information messages in broadcasts to the mobile devices. Each mobile device receives the system messages and adjusts its settings accordingly.
In Universal Mobile Telecommunication System (UMTS) and Long Term Evolution (LTE) systems, each of the base stations creates the system information messages and transmits the system information messages as broadcast to the devices. Each device adjusts its settings, and subsequently signals in accordance with the settings.